Growth Is Major Pollution Factor

Only recently have local and state officials taken real steps to revive the Halifax River. Its demise has taken decades, in general following the growth of the cities on its banks.

Among the river's most serious ailments:

- Sewage. The seven cities surrounding the Halifax pump 26.8 million gallons of treated sewage each day into a 12-mile stretch of the river.

Today, almost all the effluent has gone through ''secondary'' treatment, meaning almost all solid waste has been removed from the water, and it has been chlorinated to kill bacteria.

Still, the effluent adds nutrients in the form of nitrogen and phosphorous. These act as fertilizers for algea growth, which in turn robs sea grasses of sunlight.

The dead vegetation combines with oils and topsoil that have washed into the river from stormwater, creating a dark, gooey muck that further smothers plants and shellfish.

- Stormwater runoff. Heavy rain saturates soil quickly. What doesn't soak in runs off, down storm sewers and eventually out - untreated - into the Halifax.

Stormwater accounts for almost all the sediment in the river and as much nutrients (from fertilizer washed off lawns and crops) as from treated sewage. In addition, runoff accounts for almost all the toxic metals - lead, zinc, copper, chromium, cadmium - and oils in the river.

- Loss of marshland. The banks of the Halifax once were lined with a 20- to 50-foot buffer of swamp. The plants and animals living there acted as natural filters, cleaning the water that wound up in the river.

Development has destroyed much of that filter. Canals were dug to drain land next to the river, and homes and condominiums were built next to the water, separated only by a seawall.

- Construction of causeways. Road engineers found it easier to erect bridges across the nearly mile-wide river by building spits of land out into the water from either bank. These causeways have made bottlenecks out of bridge crossings, severely limiting the cleansing tidal flow through them.